Let f(x) = [ x ]. Df = R
Let a be any real number ∈ Df.
Two cases arise:
Case I. If a is not an integer, then
⇒ f is continuous at x = a
Case II. If a ∈ 1, then f(a) = [ a ] = a and
∴ f is not continuous at x = a, a ∈ I.
∴ function is discontinuous at every integral point.